Immobilization of BSA on Silica-Coated Magnetic Iron Oxide Nanoparticle

Colloid stable magnetic iron oxide nanoparticles, which undergo reversible precipitation from aqueous solution with external magnetic flux, can have many potential applications. However, the lack of generic homogeneous anchoring sites on a magnetic nanoparticle surface for binding of chemical/biochemical species under a wide range of conditions is one key problem. It is shown that a small size iron oxide nanoparticle encapsulated in a thin silica shell can offer specific sites to bind protein molecules via surface silanol groups electrostatically at pH 7.4 without severe denaturing of the bulky protein structure. As a result, we show that a high loading of bovine serum albumin (BSA) of 85 mg/g can be anchored on the silica-encapsulated iron oxide. FTIR, circular dichroism, and binding constant (using site I and site 11 drugs) measurements show only a small degree of conformational alteration upon immobilization. A partial unfolding of secondary structures on the external sheath of the protein due to competitive hydrogen bonding interactions of functional groups such as -C=O and -NH with surface acidic hydroxyl groups is shown to take place despite the use of buffered pH 7.4 solution. In contrast to the blockage of drug binding sites reported in the case of anchored BSA on extended silica surface, our results clearly show that the internal hydrophobic sites I and II of the immobilized BSA on this silica-based magnetic nanoparticle remain intact for drugs binding at a high degree.